1. Field of the Invention
The present invention relates to current sensors for measuring target current flowing through an electric wire (hereinafter, referred to as a “wire”), and in particular, relates to a current sensor including a magnetic sensing element.
2. Description of the Related Art
In the field of motor drive technology for electric vehicles and hybrid cars, relatively large current is used, and therefore current sensors capable of measuring such large current in a contactless manner are required. Such current sensors recently developed include a current sensor that allows magnetic sensor elements to detect a change in magnetic field caused by target current (refer to Japanese Unexamined Patent Application Publication No. 2006-322706, for example).
The current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2006-322706 includes a substrate with a slit having a circular end located in middle part of the substrate and four magnetic impedance elements arranged apart so as to surround a wire extending through the circular end of the slit. In the current sensor, a target current is determined on the basis of the sum of values of signals output from the magnetic impedance elements, the values varying depending on an induced magnetic field from the target current flowing through the wire extending through the circular end of the slit.
As an installation position of the current sensor is displaced relative to a wire, a magnetic flux density at the position of the sensor significantly changes. Accordingly, when the installation position of the current sensor including the magnetic impedance elements is displaced relative to the wire, the output of the sensor significantly fluctuates. The current sensor therefore has to be securely fixed to the wire. The current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2006-322706 is positioned and fixed by pressing the wire against an inner surface of the circular end of the slit.
In such a structure in which a wire is pressed against a casing (or an inner surface of a circular end of a slit) as in the current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2006-322706, the centers of wires having different diameters differ in position from one another when fixed. Unfortunately, an output may fluctuate as described above.